The present invention relates to a magnetic disk or like magnetic recording medium of the kind having a magnetic layer, or film, which is provided on a non-magnetic substrate by dry-process or wet-process plating means, and a method of producing such a recording medium.
Magnetic disks which are applicable to computer peripherals for data storage purposes may generally be classified into two types, i.e., a coated type having a magnetic layer provided on a non-magnetic substrate by a coating and a plated type having a magnetic layer deposited by a dry-process or wet-process plating means. A plated type magnetic disk features an inherently high magnetic material packing density and, therefore, is feasible for high-density recording because a magnetic layer thereof is formed not by using a binder but by depositing Co-based magnetic alloy or like composition on a non-magnetic substrate by plating means. However, the problem with such a plated type magnetic disk left unsolved is that since the easy axis within the magnetic layer provided by plating is isotropic or since it is oriented in the radial direction of the disk, playback output, resolution and other factors attainable with the disk are limited.
The question which led us to the present invention was whether a magnetic layer formed on a plated type magnetic disk by plating means was influenced in one way or another by the surface condition of an under layer during the course of formation. After research and a series of experiments, we found that the orientation of the easy axis of a plated magnetic layer is effected by the surface condition of an under coating. Specifically, to produce magnetic disks, we prepared non-magnetic substrates which were each scratched substantially concentrically or substantially helically, i.e., substantially along a direction in which a playback head reads signals. When magnetic layers, or films, were provided by plating on the so roughened surfaces of the non-magnetic substrates, they showed magnetic anisotropy having an easy axis which extends in the reading direction of a playback head, due to the influence of their underlying surface configurations.
The present invention is an achievement derived from the above-described finding.